The present invention relates to water-soluble film-forming polyurethanes, aqueous solutions thereof and processes for preparing same.
The invention further relates to the application of the products, in the form of solutions, as sizing for textiles, preferably for sizing warp threads for weaving and the application of these aqueous polyurethane solutions for bonding the flesh and grain splits of leathers.
In the textile industry there is a current trend to weave "synthetic" yarns which only have the twist thereof imparted by the frame on which the continuous filament is spun, that is to say 10 to 15 turns per meter. However, it is then necessary, to facilitate the weaving operation, to apply special high performance sizes to the yarns because it is virtually impossible to weave these low-tension yarns due to their lack of sufficient cohesion. Of course, it is also necessary that these sizes be removable by means of water before dyeing can be accomplished.
Various products have heretofore been proposed for sizing synthetic yarns, for example products based on acrylic or vinyl polymers, but these products are generally unsuitable, and specifically undesirable for application to linear polyesters, such as polyethylene terephthalates, and the performances of these products remain unsatisfactory. Other products which have been proposed are various types of water-soluble sulfonated aliphatic or aromatic polyesters. By way of example, there may be mentioned polyesters obtained from isophthalic acid, sodium dimethylsulfoisophthalate and diethylene glycol, or from isophthalic acid, sodium dimethylsulfoisophthalate, adipic acid and diethylene glycol, or from isophthalic acid, unsaturated acids (maleic acid and itaconic acid), diethylene glycol and sodium metabisulfite and the like.
The commercially available products of this type are likewise not always entirely satisfactory. In general, there are two different types of difficulties encountered in the utilization of these; namely problems in the application of same or in their preparation. Thus, the shelf life of the aqueous solutions is relatively short and the mechanical properties of the polymers are seriously inadequate if their numerical average molecular weight does not reach relatively high values. However, in seeking to obtain polymers having the necessary high numerical average molecular weights, serious technological difficulties are encountered, such as the necessity of carrying out the condensation reactions in a high vacuum and for considerable periods of time which obviously detract from the processability of these polymers and augment the expense of products derived therefrom. Another disadvantage, encountered especially with the acrylics, is the fact that these products cause a certain amount of soiling of the weaving looms.
The British Patent No. 1,128,568 discloses water-dispersible polyurethanes which are prepared from a polyester or polyamide having a molecular weight of between 600 and 20,000 and containing carboxylate and/or sulphonate groups, and polyisocyanates. These polyurethanes are insoluble in water and therefore are not useful as sizing agents.